1. Field of the Invention
The present invention relates to a method of manufacturing a micro structure and to a substrate structure, and more particularly, to Micro Electro Mechanical System (MEMS) technology and a substrate structure suitable for manufacturing a micro structure having a height of the micrometer (μm) order or the nanometer (nm) order, such as bumps for electrical connections, flow channel structures for passing fluid, and various devices.
2. Description of the Related Art
Japanese Patent Application Publication No. 06-077229 discloses a method of forming a bump (which corresponds to a micro structure) on an electrode pad arranged on a semiconductor device on a wafer, in which a height positioning seat is arranged as a core member inside the bump in order to increase the positional accuracy in the height direction of the bump. The height positioning seat used as the core member is made of a material that does not melt at the melting point of the bump material (Pb—Sn 60 wt %), and when the bump material is melted in bonding process of the semiconductor device and a circuit board, the height positioning seat acts as a spacer in the height direction and maintains a prescribed dimension. Japanese Patent Application Publication No. 06-077229 describes only the relationship between the melting points of the inner material (height positioning seat) and the outer material (bump material), as material properties. However, the relationship between other factors is not specified, and it may not be possible to achieve sufficient flatness according to differences in hardness between the inner material and the outer material.
Japanese Patent Application Publication No. 06-209028 discloses a method including a step of pressing the upper faces of bumps formed on a semiconductor chip with a pressing tool having a flat pressing face so as to achieve uniform height of the bumps before mounting the semiconductor chip on a substrate, in order to reduce contact defects caused by variation in the height of the bumps. This method requires the pressing tool in order to achieve uniform bump height, and the manufacturing process is complicated. Moreover, there are cases where it is not possible to sufficiently eliminate height non-uniformities (variations) by means of the pressing method.
Japanese Patent Application Publication No. 2005-216508 discloses a composition of a metal paste capable of forming bumps having little variation in hardness and a suitable soft hardness, and a method of forming bumps using the metal paste. According to this method, flexible bumps (bumps which are soft as possible within the required hardness range) are manufactured by using the metal paste that does not contain glass frit and by adjusting the calcination density. In this method, when manufacturing bumps having a low calcination density, there is a problem in that the strength of each column (bump) is insufficient, and so on. Furthermore, Japanese Patent Application Publication No. 2005-216508 makes no mention of a method for making the height of the bumps uniform and there may be cases where the bumps cannot be bonded parallel when the substrates are pressed to each other.
WO 2004/061935 discloses a method including a cutting process using a bit in order to level the height of fine bumps formed on a substrate. In this method, the leveling is performed in such a manner that the surfaces of bumps and the surface of an insulating film (resist mask) are continuous and flush, by employing the cutting process using the bit instead of chemical mechanical polishing (CMP), whereupon the insulating film is removed. However, the steps involved in this method are complicated, and cut debris, and the like, arises and can cause contamination.
In various micro structures which are not limited to the bumps described above, if the height of a micro structure is relatively high and a substrate, or the like, is bonded thereon, then height non-uniformities (uneven height) present a problem. Moreover, if a micro structure has narrow width and large height and is bonded by application of pressure, then the column portions of the micro structure bend and break during the course of bonding, and accurate bonding is not possible.